1. Field of the Invention
The present invention relates to a monolithic ceramic electronic component such as a monolithic ceramic capacitor, and more particularly to an improvement in an inner electrode of the same.
2. Description of the Related Art
Conventionally, dielectric ceramic materials such as barium titanate, strontium titanate, calcium titanate, and the like, having a perovskite-type structure have been widely used as capacitor materials, due to their high dielectric constants. With the recent tendency that electronic components are small-sized, capacitors, which are passive components, are required to have a high electrostatic capacitance and also to be miniaturized.
For monolithic ceramic capacitors containing ceramic dielectric materials in their dielectric layers, it is necessary to bake the dielectric ceramic materials at high temperatures, for example, at about 1300.degree. C. in the atmosphere. Therefore, as the inner electrodes, noble metals such as palladium, platinum, and the like, and their alloys were used. However, these electrode materials are very expensive, and the material cost occupied a large part of the product cost. Thus, it was difficult to reduce the product cost.
To solve the above-mentioned problems, it has been attempted to use base metals as a material for the inner electrodes of the monolithic ceramic capacitors. As a result, there have been developed a variety of dielectric ceramic materials which have such anti-reduction properties that they can be baked in a neutral or reducing atmosphere, which prevents the electrodes thereof from being oxidized. Such base metals as the inner electrode material include cobalt, nickel, copper, and the like. In the viewpoint of the cost and the anti-oxidation properties, nickel is mainly used.
At present, there is still a need to develop still smaller-sized and higher-capacitance monolithic ceramic capacitors. For this reason, investigation has been made on dielectric ceramic materials having a higher dielectric constant and on thinner ceramic layers made of dielectric ceramic materials. Furthermore, examination has been made on thinner electrodes.
In general, the inner electrodes of the monolithic ceramic capacitors are formed by printing, such as screen-printing, of pastes containing metal powders. For example, in most cases, nickel powders for use as the metal powder to be contained in such pastes, formed by liquid phase method or chemical vapor deposition method, have a mean particle size exceeding 0.25 .mu.m. However, since the particle size is large, it is difficult to form the thin inner electrodes.
When the nickel powder having a mean particle size of about 0.25 .mu.m were used, the thickness of the inner electrode was required to be at least 0.8 .mu.m to realize the dielectric characteristics of the dielectric ceramic materials.
For the purpose of enhancing the electrostatic capacitance of the monolithic ceramic capacitors, one of the most effective means is to provide a thin ceramic layer between the inner electrodes. However, if the ceramic layer has a thickness of 3 .mu.m or less when the inner electrodes each have a thickness of 0.8 .mu.m, delamination is often caused due to the difference in shrinkage between the inner electrode material and the ceramic. This is one of fatal defects of the monolithic ceramic capacitors.
In the case that the nickel power and/or the ceramic raw material powder has a large mean particle size, large concavities and convexities at the interfaces between the inner electrodes and the ceramic layers are formed. When the powders are baked, this causes the problem that the coverage (effective electrode areas) of the inner electrodes is reduced (with an increase in the frequency of electrode breaking). Thus, this brings the reduction in reliability of the monolithic ceramic capacitor.